Multi-Messenger Astrophysics and Fundamental Physics Tests with Gravitational Waves

先进的LIGO探测器已经实现了直接探测引力波的长期目标，这与爱因斯坦广义相对论的百年预言相一致。2015年底对最初几个信号的戏剧性探测也让我们意识到黑洞的存在，这些黑洞的质量高达太阳质量的36倍，它们的双星轨道距离足够近，可以以引力波的形式释放出巨大的能量。然而，这仅仅触及了引力波信号可能存在的表面，以及我们可以从中学到什么。随着先进的LIGO探测器的改进，该奖项支持的研究将充分利用新的能力，意大利、日本和最终印度的类似设施也将加入其中。目标是加强与更广泛的天文学界的交流与合作，使天文学界能够利用所有现代天文学工具，从地面上的光学和射电望远镜到航天器上的x射线和伽马射线探测器，通过它们可能发射的电磁能和/或中微子来发现和研究LIGO引力波信号的来源。具体来说，这项工作将有助于改进分析软件和程序，以便在更好的监测下更迅速、更可靠地选择有希望的事件，并对强烈、明确的事件及时发出公共警报。这个小组将合作寻找与引力波事件相匹配的伽马射线、x射线和无线电爆发，并探索如何最好地利用不断增长的引力波探测器网络来搜索“标量”引力波爆发，这将是一个独特的迹象，表明爱因斯坦的理论并不是关于引力的全部故事。最后，PI将分享他的专业知识，并通过家庭探索日外展计划为孩子和他们的父母提供有趣和有教育意义的实践活动，以了解科学。LIGO-Virgo的“EM后续项目”已经招募了90多个合作团体，他们对引力波事件和候选对象做出了强烈的反应，但该项目的几个技术方面需要改进。基于该小组在当前事件选择和警报生成软件和程序方面的经验，PI将帮助重新实施系统，使其更快、更健壮、更易于监控，并准备好在未来先进引力波探测器网络的观测运行中生成公共和私人警报。该小组目前正在与LIGO和Virgo的合作者讨论如何最好地管理系统设计、软件开发和测试。与此同时，他们正在与费米任务科学小组和LWA射电天文台的用户合作，以触发和非触发搜索模式搜索伽马射线暴和可能与引力波信号对应的无线电瞬变信号。根据各种模型，涉及至少一颗中子星的双星合并可能会产生电磁波谱上的辐射，尽管它们可能很难探测到并最终确定是对应的。双黑洞合并是否会产生可探测的辐射，就像LIGO迄今探测到的事件一样，仍然是一个悬而未决的问题。为了测试广义相对论（GR）是否是正确的重力理论，PI将使用WaveBurst算法的改进版本来搜索具有标量应变偏振的引力波爆发，这与作为GR标志的张量偏振状态不同。该小组将研究全天和位置约束（当可能的对口已被确定时）搜索；后者还可以用来测试引力波是否以光速传播（正如GR所预测的那样）。

The Advanced LIGO detectors have achieved the long-sought goal of directly detecting gravitational waves, in line with a century-old prediction of Einstein's general theory of relativity. The dramatic detection of the first few signals in late 2015 also opened our ears to the existence of black holes with up to about 36 times the mass of our sun, in binary orbits close enough to merge with a huge release of energy in the form of gravitational waves. However, this has only scratched the surface of what gravitational-wave signals may be out there and what we can learn from them. The research supported by this award will take full advantage of the new capabilities as the Advanced LIGO detectors improve and are joined by similar facilities in Italy, Japan and eventually India. The goal is to enhance communication and cooperation with the broader astronomy community so that the astronomical community can use all the modern tools of astronomy, from optical and radio telescopes on the ground to X-ray and gamma-ray detectors on spacecraft, to find and study the sources of LIGO's gravitational-wave signals through the electromagnetic energy and/or neutrinos that they may also emit. Specifically, this effort will help to improve the analysis software and procedures to select promising events more rapidly and reliably, with better monitoring, and to produce prompt public alerts for strong, clear events. This group will collaborate on searches for gamma-ray, X-ray and radio bursts matching up with gravitational-wave events, as well as explore how best to use the growing network of gravitational-wave detectors to search for "scalar" gravitational-wave bursts, which would be a distinctive sign that Einstein's theory is not the whole story about gravity. Finally, the PI will share his expertise and develop fun and educational hands-on activities for children and their parents to learn about science through a Family Discovery Days outreach program. The LIGO-Virgo "EM follow-up program" has enlisted over 90 partner groups who have shown a strong response to the gravitational-wave events and candidates shared with them so far, but several technical aspects of the program need improvement. Building on this group's experience with the current event selection and alert generation software and procedures, the PI will help re-implement the system to be faster, more robust, easier to monitor, and ready to generate both public and private alerts during the future observing runs of the advanced gravitational-wave detector network. This group is currently discussing with LIGO and Virgo collaborators how best to manage the system design, software development and testing which will be needed. In parallel, they are working with the Fermi mission science team and LWA radio observatory users to search for gamma-ray bursts and radio transients that may be the counterparts of gravitational-wave signals, in both triggered and un-triggered search modes. According to various models, binary mergers involving at least one neutron star are likely to produce emissions across the electromagnetic spectrum, although they may be challenging to detect and to definitively identify as the counterpart. It remains an open question whether binary black hole mergers, like the events detected by LIGO so far, produce detectable emissions. To test whether general relativity (GR) is the correct theory of gravity, the PI will use a modified version of the WaveBurst algorithm to search for gravitational-wave bursts with a scalar strain polarization, distinct from the tensor polarization states which are the hallmark of GR. The group will investigate both all-sky and position-constrained (when a possible counterpart has been identified) searches; the latter can also enable a test of whether the waves travel at the speed of light (as predicted by GR) or not.